Labour introduced the controversial charges while in government with Fine Gael. But their party chairman, Willie Penrose, has published a draft law allowing for a full return of all money paid to Irish Water by customers within six months.

Former Labour Environment Minister Alan Kelly said scrapping water charges was "environmental treason" by Fianna Fáil, who forced the change as the price of facilitating the incoming minority Government. Mr Kelly, tipped by many to be the next party leader, has also expressed doubt about the administrative challenge of refunds which are entangled with the €100 water grant already paid out.

Launching the "Water Charges (Fair Treatment of Customers) Bill 2016", Mr Penrose said that if water charges are suspended, Labour will champion equal treatment of those who paid and those who did not pay.

"We cannot allow a situation to arise where people who comply with the law of the land, are left feeling they have been mugged," the Westmeath TD said.

Mr Penrose, also a leading barrister, said that if the party's bill is not accepted he will proceed with his threat of a class action on behalf of citizens who have paid their water charges. The Labour strategy in opposition, of championing the case of the six out of 10 citizens who paid some water bills, is the latest change of political position on the issue.

During the 2011 general election, Labour warned that a Fine Gael-only government would introduce a €238 per year water tax. After much internal acrimony, yearly rates of €160 for a one-person household, and €260 for others, were introduced in 2014 by the Fine Gael-Labour coalition following big street protests.

Back in December 1994, as they entered the Rainbow Coalition, Labour abandoned the principle of water charges fearing a big backlash from opponents on the further left of the political spectrum.